Science Ticker

TIME LAG Zika infections among pregnant women (solid line and scale on left) in Colombia spiked in January (around week 4). About six months later, the country saw a drastic increase in the number of infants and fetuses with microcephaly (dotted line and scale on right).

“This provides very compelling evidence that every country that experiences a large Zika outbreak is likely to see devastating outcomes on fetuses and infants,” says CDC epidemiologist Peggy Honein.

Microcephaly cases in 2016 reached a high point in Colombia in July, about 24 weeks after Zika virus infections peaked there. The time lag suggests that Zika poses the greatest risk to pregnant women in the first and early second trimester, the authors write.

Colombia’s dramatic uptick in microcephaly cases follows one reported in Brazil, which, in 2015, experienced a ninefold increase in cases compared with the previous 14 years. Scientists have concluded that Zika virus was a causal factor.

Some researchers wondered, though, about the extent of Zika’s role in microcephaly in Colombia. Earlier this year, the country’s tally of microcephaly cases seemed smaller than expected, given the reported rise in Zika infections.